1. Field of the Invention
The present invention relates to motor controllers for electromotive power steering systems that perform power-assisted steering by applying torque generated by a motor to a steering mechanism.
2. Description of the Related Art
An electromotive power steering system has conventionally been known, in which torque generated by a motor such as a three-phase brushless motor is transmitted to a steering mechanism, perform power-assisted steering. See. e.g., Japanese Laid-Open Patent Publication 187,578/2001.
Relationships between a motor M for assisting this electromotive power steering system and a microcontroller C for controlling the motor M are illustrated in FIG. 7, and a block diagram representing a functional configuration of a motor controller for a conventional electromotive power steering system is illustrated in FIG. 8.
FIG. 8 represents the relationships among the microcontroller C for controlling the conventional electromotive power steering system, values inputted into the microcontroller C, and the motor M that the microcontroller C controls. The motor M, (not illustrated), assistively supplies torque to the electromotive power steering system, and the motor M is driven by a power circuit 52 that is controlled by the microcontroller C. Here, a vehicle speed V obtained by a vehicle speed sensor 42, steering torque T obtained by a torque sensor 43, and a rotor angle θre of the motor M detected by a resolver R connected to the motor M and by a rotor-angle detecting circuit 45 are inputted into the microcontroller C. Moreover, because the motor M is controlled with electric current feedback being applied thereto by the microcomputer C, the electric current (U-phase current iua, V-phase current iva) flowing through the motor M, detected by a motor-current detector 41 (a U-phase current detector 41u, a V-phase current detector 41v), is inputted into the microcontroller C.
Next, FIG. 9 is explained. In this motor controller, the vehicle speed V detected by the vehicle speed sensor 42 and the steering torque T that has been detected by the torque sensor 43 and phase-compensated through a phase-compensation circuit 44 are inputted into the microcontroller C. Moreover, the motor controller is provided with a target current calculator 61 for determining a target current command value Ia*′ (an effective current value flowing through the U-phase, V-phase, and W-phase) by which current is applied to the motor M. In order to improve the steering feel, a convergence correction value Ico*, is calculated from the vehicle speed V and a rotor angular rate ωre. ωre is obtained by a rotor angle θre of the motor M, detected by the resolver R and a rotor angular detecting circuit 45, as passed through a rotor angular rate calculator 65. The convergence correction value is given to an adder 62. In the adder 62, the target current command value Ia*′ (the effective value), inputted from the target current calculator 61, and the convergence correction value Ico*, inputted from convergence corrector 64, are summed, and a convergence-compensated target-current command value Ia* is set, which represents the amplitude of current (sine wave current) to be applied to the U-phase, V-phase, and W-phase of the motor M. Moreover, in order to enable the current value to be treated as a dc current amount independent from the rotor angle θre of the motor M, in a q-axis current command value calculator 66, a q-axis current command value iqa* is determined with a d-q coordinate conversion being applied to the target current command value Ia* after the convergence correction has been performed. On the other hand, a d-axis current command value ida* is set to zero.
The d-axis current command value ida* and the q-axis current command value iqa* are inputted into subtractors 67d and 67q, respectively. These subtractors 67d and 67q are constituted so that a d-axis current detection value ida and a q-axis current detection value iqa are given, which are obtained by passing the output from the U-phase current detector 41u for detecting the U-phase current iua that actually flows in the U-phase of the motor M, and the output from the V-phase current detector 41v for detecting the V-phase current iva that actually flows in the V-phase, through a three-phase AC/d-q coordinate transformer 68. Consequently, from the subtractors 67d and 67q, deviations for the d-axis current command value ida* and the d-axis current detection value ida, and deviations for the q-axis current command value iqa* and the q-axis current detecting value iqa, are outputted, respectively.
The deviations outputted from the subtractors 67d and 67q are applied to a d-axis current PI (proportional integration) controller 69d and a q-axis current PI controller 69q; whereby a d-axis voltage command value Vda* and a q-axis voltage command value Vqa* are obtained, respectively.
The d-axis voltage command value Vda* and q-axis voltage command value Vqa* are inputted into a d-q/three-phase AC coordinate transformer 72. The rotor angle θre detected in the rotor angle detecting circuit 45 has been also inputted into this d-q/three-phase AC coordinate transformer 72; therefore, the d-q/three-phase AC coordinate transformer 72 transforms, in accordance with the following equation (1), the d-axis voltage command value Vda* and q-axis voltage command value Vqa* into command values Vua* and Vva* in the three-phase AC coordinate system, respectively. Then, the U-phase voltage command values Vua* and V-phase voltage command value Vva* obtained are inputted into a three-phase PWM (pulse width modulation) modulator 51.
                                                                        [                                                                                                    V                        va                        *                                                                                                                                                V                        ua                        *                                                                                                                                                V                        wa                        *                                                                                            ]                            =                            ⁢                                                                    [                    C                    ]                                                        -                    1                                                  ⁡                                  [                                                                                                              V                          da                                                                                                                                                              V                          qa                                                                                                      ]                                                                                                        =                            ⁢                                                                                          2                      3                                                        ⁡                                      [                                                                                                                        cos                            ⁢                                                                                                                  ⁢                                                          θ                              re                                                                                                                                                                                          -                              sin                                                        ⁢                                                                                                                  ⁢                                                          θ                              re                                                                                                                                                                                                        cos                            ⁡                                                          (                                                                                                θ                                  re                                                                -                                                                                                      2                                    ⁢                                    π                                                                    3                                                                                            )                                                                                                                                                            -                                                          sin                              ⁡                                                              (                                                                                                      θ                                    re                                                                    -                                                                                                            2                                      ⁢                                      π                                                                        3                                                                                                  )                                                                                                                                                                                                                                      cos                            ⁡                                                          (                                                                                                θ                                  re                                                                -                                                                                                      4                                    ⁢                                    π                                                                    3                                                                                            )                                                                                                                                                            -                                                          sin                              ⁡                                                              (                                                                                                      θ                                    re                                                                    -                                                                                                            4                                      ⁢                                      π                                                                        3                                                                                                  )                                                                                                                                                                          ]                                                  ⁡                                  [                                                                                                              V                          da                                                                                                                                                              V                          qa                                                                                                      ]                                                                                        (        1        )            
However, a W-phase voltage command value Vwa* is not calculated in the d-q/three-phase AC coordinate transformer 72, but rather in a W-phase voltage command value calculator 73, on the basis of the U-phase voltage command value Vua* and V-phase voltage command value Vva* that have been calculated in the d-q/three-phase AC coordinate transformer 72. That is, in the W-phase voltage command value calculator 73, the U-phase voltage command value Vua* and V-phase voltage command value Vva* are inputted, and, in the W-phase voltage command value calculator 73, a W-phase voltage command value Vwa* is obtained by subtracting from zero the U-phase voltage command value Vua* and V-phase voltage command value Vva*.
The W-phase voltage command value Vwa* calculated in the W-phase voltage command calculator 73, similarly to the U-phase voltage command value Vua* and V-phase voltage command value Vva*, is applied to the three-phase PWM modulator 51. The three-phase PWM modulator 51 generates PWM signals Su, Sv, and Sw corresponding to the U-phase voltage command value Vua*, V-phase voltage command value Vva*, and W-phase voltage command value Vwa*, respectively, and the generated PWM signals Su, Sv, and Sw are outputted to the power circuit 52. Thereby, voltages Vua, Vva, and Vwa, corresponding to the PWM signals Su, Sv, and Sw, are applied to the U-phase, V-phase, and W-phase, respectively of the motor M, whereby the motor M generates torque required for the power-assisted steering.
Moreover, in the above described prior art, an abnormality judging unit 74 is provided, for judging whether an abnormality such as an offset has occurred. The unit 74 is configured to judge, on the basis of the d-axis current detection value ida and q-axis current detection value iqa outputted from the three-phase AC/d-q coordinate transformer 68, whether an abnormality has occurred. Provided that the U-phase current iua, V-phase current iva, and W-phase current iwa each have an amplitude Ia, the d-axis current ida and the q-axis current iqa are expressed by the following equation (2), which is understood to be independent of the rotor angle θre. Therefore, the abnormality judging unit 74 can acquire the d-axis current ida and the q-axis current iqa without regard to the rotor angle θre, and determine, on the basis of the acquired d-axis current ida and the q-aixis current iqa, whether or not an abnormality is present. It is described in this document that the effective value of the current flowing through the motor M also need not be calculated.
                              [                                                                      i                  da                                                                                                      i                  qa                                                              ]                =                  [                                                    0                                                                                                          -                                                                  3                        2                                                                              ⁢                                      I                    a                                                                                ]                                    (        2        )            
However, in the above described prior art, no concrete practical method for the abnormality judgment is described at all. That is, it is not described, for example, which portion of the amplitude Ia, the d-axis current detecting value ida and the q-axis current detecting value iqa are used.
Therefore, an objective of the present invention is to provide a concrete practical means for easily performing abnormality judgments in a motor control system for electromotive power steering systems.